Webs, such as paper, paperboards, and polymer films which have been coated with an extruded polymer resin find use in numerous applications, particularly in packaging materials. In many such applications, it is the properties of the polymer coating which are most important such as heat sealing or the ability to provide a barrier against liquids or vapors. High strength and weight or bulk in the substrate web are sometimes of secondary importance, and a lightweight substrate may even be preferred in some applications.
Although lightweight webs with certain properties may be suitable or preferred in many applications, relatively heavyweight webs are often used because lighter materials cannot be satisfactorily processed in an extrusion coating process. The extrusion coating process subjects the web to relatively severe conditions including tension, exposure to hot molten extrudate, and high nip pressures while the web is transferred from an unwind roll, through the extruder, and onto a windup roll. As a result, attempts to extrusion coat lightweight substrate webs have resulted in excessive web breaks and unacceptable stretching and deformation of the substrate.
It is therefore an object of the invention to provide a method for extrusion coating lightweight web materials with a polymer coating.
Another object of the invention is to provide a relatively low basis weight, extrusion coated web.
Still another object of the invention is to provide a method of making a lightweight web having an extrusion coating without excess web breakage, deformation, or stretching during the extrusion process.